Light-emitting device, light-emitting apparatus, electronic device, and lighting device

Abstract

A light-emitting device with a long lifetime is provided. In a light-emitting device that includes an EL layer between a pair of electrodes, a light-emitting layer included in the EL layer has a functional stacked-layer structure, whereby the efficiency and reliability of the light-emitting device can be increased.

The invention claimed is: 
     
       1. A light-emitting device comprising:
 an anode; 
 a cathode; and 
 an EL layer between the anode and the cathode, 
 wherein the EL layer comprises a hole-injection layer, a hole-transport layer, a light-emitting layer, and an electron-transport layer, 
 wherein the hole-injection layer is in contact with the anode, 
 wherein the light-emitting layer comprises a first light-emitting layer and a second light-emitting layer, 
 wherein the first light-emitting layer is in contact with the hole-transport layer, 
 wherein the second light-emitting layer is in contact with the electron-transport layer, 
 wherein the first light-emitting layer comprises a first compound and a second compound, 
 wherein the second light-emitting layer comprises a third compound and a fourth compound, 
 wherein the hole-injection layer comprises a fifth compound and a sixth compound, 
 wherein the fifth compound has an electron-withdrawing group, 
 wherein the sixth compound has a HOMO level higher than or equal to −5.7 eV and lower than or equal to −5.4 eV, 
 wherein the hole-transport layer comprises a seventh compound, 
 wherein the seventh compound has a HOMO level lower than the HOMO level of the sixth compound and higher than a HOMO level of the second compound, 
 wherein the electron-transport layer comprises an eighth compound and a ninth compound, 
 wherein the eighth compound is an organometallic complex of an alkali metal or an alkaline earth metal, and 
 wherein the ninth compound has a HOMO level higher than or equal to −6.0 eV. 
 
     
     
       2. The light-emitting device according to  claim 1 ,
 wherein each of the first light-emitting layer and the second light-emitting layer emits blue light. 
 
     
     
       3. The light-emitting device according to  claim 1 ,
 wherein the electron-transport layer comprises a first portion and a second portion, 
 wherein the second portion is located between the first portion and the cathode, and 
 wherein a ratio of the eighth compound to the ninth compound in the electron-transport layer differs between the first portion and the second portion. 
 
     
     
       4. The light-emitting device according to  claim 3 ,
 wherein a proportion of the eighth compound in the electron-transport layer is lower in the second portion than in the first portion. 
 
     
     
       5. The light-emitting device according to  claim 1 ,
 wherein the first compound and the third compound are the same light-emitting compound. 
 
     
     
       6. The light-emitting device according to  claim 1 ,
 wherein the second compound and the fourth compound are the same compound.